【作者】 孙昭华；

【导师】 李义天；

【作者基本信息】 武汉大学 ， 水力学及河流动力学， 2004， 博士

【摘要】 世界各国河流开发历史和经验教训表明,由于对人类活动引起水沙条件变化后河流系统的调整机理认识不足,流域开发中普遍引起某项或多项河流功能受损或衰竭。造成这种现象的深层原因,一是对河流系统中水、沙、河床之间的整体联系和互相影响的机理认识不足,导致河流系统中出现意想不到的现象和负面效应;二是对水沙变化和河流系统调整的后续环境、生态和社会效应认识不足,在保障或优化某项河流功能的同时,却导致河流系统整体健康的损害。因此,从整体上研究水沙变异条件下河流系统的调整机理,对于河流健康的保障具有重要意义。保持河流各方面整体协调是流域开发研究的重点和必然趋势。然而,目前相关的研究大多是针对河流功能受损后的修复和防护,而对于水沙调节可能引起的河流系统功能调整研究甚少。大量事实表明,当人们意识到各种工程对河流系统的影响时,往往河流系统功能已受到明显损伤,对河流系统自然、生态环境的修复和重建是十分困难甚至不可能,防患于未然胜于任何补救措施。水沙变异后河流系统调整涉及领域广,时空跨度大。当前的研究已经在各相关领域中开展了相当广泛而深入的工作,但这些成果往往是从不同的角度出发,具有不同的时空尺度,而且由于是在单学科内结合河流系统的单方面属性开展,对相互之间的因果制约以及层次关系缺乏深入的认识,不利于对河流系统整体调整趋势的预测和分析。本文以水沙变异为主线,遵循从原因至结果的顺序,力图建立不同变化与河流系统不同响应之间的联系,以便最终能够达到根据水沙变化而预测河流系统功能调整的目的。研究的特色在于,同时注重了河流系统动力特征、形态特征的动态变化及其防洪、生态等方面的效应,为河流系统调整预测和功能评估打下基础。论文对水库下游的泥沙输移、河型转化、浅滩演变等方面开展了深入研究,并对河流系统调整对区域整体的防洪形势、生态环境状态影响进行了详细讨论,是从不同方面、不同尺度同时研究河流系统的首次尝试,在河流系统动力与形态、微观与宏观、地貌与生态等变化的层次性、联系性方面得到了一些有益的认识。同时,论文结合了长江三峡下游的实际背景,一些结论对于长江水资源开发过程中河流系统功能的整体维持具有参考价值。全文主要讨论了以下几个方面的问题:(1)分析了水沙变异与河流系统的作用特性,明确了河流系统各方面的调整实际上是系统输入特性的不同方面变化造成的;回顾了对河流系统及其功能的认识过程与研究现状,说明了建立水沙变化与河流调整对应关系的意义和必要性。(2)鉴于目前对水库下游泥沙输移特征未形成明确的统一认识,本文以大量实测资料证明:水库下游的泥沙输移能力不可能超出建库前的天然水平,全沙和分组输沙量都符合这个规律,而且与水库运用方式、下游河床形态调整等因素无关。基于水库下游泥沙输移变化一般特征,讨论了黄河小浪底调水调沙的可行性和三峡下游冲刷冲淤计算的合理性。利用水库调水调沙使下游河道输沙能力超过天然水平的尝试是值得斟酌的;目前对三峡下游的冲淤预测结论中,冲刷发展进程和冲淤分布存在值得商榷之处。(3)分析了水、沙过程各种特征因素对河型过程的影响,明确水、沙、河床边界在河型塑造过程中的地位与作用。根据丹江口等水库下游水沙变异特点,分析总结了不同变异情况下可能发生的河型调整;结合三峡下游水沙条件的变化以及河型转化的机理,预估了不同河型区段的变化趋势:下荆江河段建库后首先发生下切,但由于流量增大的影响,冲刷将主要转为侧蚀,曲率有所增大。对于城陵矶以下的稳定江心洲河段而言,对流量变幅比较敏感,但由于建库前后流量变幅差别不大,而且距坝距离较远,沙量恢复程度高,因此不会发生明显的河型变化。(4)以往对浅滩演变的研究多是针对个别浅滩特例,不够系统。文中尝试从水沙条件和河床形态的角度分析浅滩演变的实质,认为浅滩的主要影响因素是河床局部形态,河段挟沙力与来沙量二者之间的跟随性差是形成浅滩的主要原因,提出了通过断面挟沙力随流量变化的指数值来判别浅滩恶劣程度的认识。结合丹江口水库下游相关资料,总结了水沙变异条件下不同特征河段浅滩的变化规律;分析总结了天然情况下长江中下游浅滩成因并预估三峡建库后演变趋势。(5)文中分析了修建水库对下游洪水过程时空分异性的影响,并以三峡下游为例开展了深入讨论。采用多种方法推求长江中游各种组合类型的典型洪水,为复杂区域的设计洪水推求提供参考,以此为基础,比较了三峡调节作用、下游的河道冲淤对中游各类型洪水过程的影响,三峡建库后前20年,长江中游尤其是城陵矶附近洪水形势依然严峻。总结流域洪水泥沙过程模拟与调控方法,文中建立了适用于复杂大型河网的泥沙数学模型,水流、泥沙系数矩阵均可分组求解,提出了多种汊点分沙模式。(6)分析了修建水库等水沙调节措施对下游河流生态环境影响的时空范围、作用方式;深入分析了生态需水量的概念内涵与基本要素,对各种估算方法的原理、适用性等进行了比较。文中一定程度上也对河流地貌—生态系统之间的联系,生态环境的层次分级,状态评估指标确定原则等进行了探讨,为今后研究打下基础。(7)探讨了如何利用水沙、河床、生态等各方面信息对河流系统整体功能进行评估,限制水沙过程最大调节程度的途径。全文主要从水沙变异的角度讨论了河流系统的调整机理,强调了调整过程的层次性、关联性、时空分异性等特征,为水沙变异条件下河流系统功能预测和评估打下初步的基础。更多还原

【Abstract】 Global experience of river development history show that river function degradation were commonly during the course of water resources exploitation, due to the absent knowledge of river system response to human disturbance on natural water-sediment regimes. Two reasons underlie the present situation: one for insufficient recognition of the linkages and interaction between water, sediment, and river morphology, which arise unexpected phenomena or negative effects in river system; another for the partial understanding of environmental, social-economical impact of river alternation, certain riverine function is improved at the cost of health degradation of the whole system. Lots of facts indicate that river system functions were often notably affected before human recognition of influence of dam and other constructs. As restoration of riverine ecosystem is very difficult or even impossible, protection measures are more needed than remediation.River system is typically a complex open system, in which the variation of input variables of water and sediment will introduce adjustment of various aspects of the whole system. Processes of“impact and response”are all over the adjustment: changes of some features of flow &sediment regime induce some corresponding consequences of hydrological, hydraulic, morphologic or ecological aspect, thereby cause the change of related riverine functions. River system interaction with flow &sediment alternation covers problems of large variety, which range over vast time and space scales. Previous researches were comprehensive and intensive carried out in many fields, but most of them were from the view of different interests, and have different temporal and spatial scales. Furthermore, because most researches were specialized in single field and associate with single aspect of the system, the cause-effect linkages and hierarchy structure were unclear, as is not fit for trend prediction and holistic evaluation at riverine system scale.Researches in this paper try to find the linkage between variation of flow &sediment regime and riverine system adjustment phenomena, which is fundamental works for prediction of riverine functions, dynamic process of river system and its effects on flood control and ecosystem are considered. Main work in this paper can be divided into four parts: firstly, analysis of the changes of flow &sediment regime due to dam alternation and feature of downstream sediment transportation; secondly, river morphology change owing to flow &sediment regime variation, such as channel pattern and shoals; thirdly, analysis of the flood and ecosystem situation in the new riverine environment; fourthly, preliminary discussion of methodology of riverine functions evaluation and protection. Most work is with the background of downstream of the TGP (Three George Project), some key issues are shown as following:(1) The characteristics of interaction between flow &sediment regime and river system is clarified. With a review of the previous research about river system and its functions, it is concluded that establishment of linkages between variation of flow &sediment regime and riverine system adjustment phenomena is necessary and significative.(2) In the paper, a description of downstream flow &sediment regime from dams is given, which is likely to affect hydrological, hydraulic, geomorphologic or ecologic aspects of rivers.In view of the absent knowledge of sediment transportation character downstream dams, we made a statistical comparison with field data to show that the transportation capacity of down stream cannot exceed the value of pre-dam period under natural situation. This rule is observed in the data of both full size sediment and each grain group, which has little relation with the type of dam operation and downstream channel morphological adjustment.According to the common phenomenon of sediment transportation downstream dams, both feasibility of flow &sediment regulation in the Xiaolangdi reservoir on Huanghe River and rationality of degradation prediction downstream the TGP is discussed. Result shows that, the attempts to increase sediment transport capacity to exceed its natural value need more consideration, and the erosion process downstream the TGP is improbable.(3) Some variables and their interaction with river channel pattern process is analyzed, including range of flow variation, rising/falling rate of flood peak, load amount, sediment particle feature and etc, the role and function of flow &sediment regime and boundary condition is also clarified. With the field data of Danjiangkou dam, the relation between flow alternation and corresponding channel adjustment is classified, based on which the probable channel response downstream the TGP is outlined. Down reach of the Jingjiang river will undergo a bed erosion process immediately after the dam closure, with the gradually discharge increment, bank erosion will dominate the process, and the planform tend to sinuous. The bar-braided reach downstream Chenglingji is unlikely to experience any notable change for the unaltered flow &sediment regime.(4) Previous researches about shoals were often case studies, and there has been no comprehensive analysis of all types. In this paper, we try to summarize the key factor in the evolution of shoals among flow &sediment regimes and local channel morphology; the result indicates the latter plays the pivotal role. The difference between sediment carrying capacity and arriving sediment amount is the main cause of shoals, thus the exponent of sediment carrying capacity changing with discharge variation can be taken as index to indicate the level of shoal state.Using the data of Danjiangkou dam as reference, relation between the change of flow &sediment regime and shoals adjustment in different type of reach section is concluded, based on which, the probable trend of shoals adjustment downstream the TGP is predicted.(5) Flood situation downstream dams both in temporal and special scope are discussed with the background of the middle reach of the Yangtze River. Multi approaches are adopted to design the flood composition of typical flood type of this region. With the result of this part of work, flood situation change owing to the influence of dam regulation and channel bed degradation (or aggradation) is estimated separately. During the early 20 years of reservoir operation, the tense flood control situation will not be much released.Reviewed the simulation methodologies of flood &sediment transportation in regional scale, a mathematical model to simulate sediment transport in complex river network is introduced, in which sediment transport equations can be solved by gradation method with junctions group divided. Measures to solve sediment diversion at junction node are also discussed.(6) In the paper, we illustrated how altering flow &sediment regime affect downstream riverine ecosystem and its temporal and special scope. After an analysis of the concept of environmental flow and its basic factors, the principle and application of each methodology is compared.(7) It is prospected about how to make multi attributes evaluation of riverine functions with the information of all aspects, and how to limit the flow &sediment regime alternation to meet the goal of river management.Discussion in this paper is most of qualitative, and the aim is to give a description of flow &sediment regime alteration and the consequent river system adjustment of multi aspects, which will serve as foundation for the prediction of river function change under flow regulation.更多还原